FILLET AND CHAMFER : WHY AND WHEN TO USE IT ??

Fillet is a round corner whereas chamfer is a slant face created at the corner. 

Even though both perform same function selection of chamfer or fillet depends on how the component is manufactured.We will discuss why and when they are used while creating parts in this article.

Comparison Between Chamfer and Fillet for External Edges :

Whether we choose to select a chamfer edge, or a fillet edge, it will often depend on factors of project such as budget and time constraints. The chart below compares some of these considerations:

When to use them ?

Fillets give a part better flow and less resistance. Using a fillet also eliminates any sharp edges that can be easily damaged, or that could cause injury when the part is handled. This means there is less risk of failing an inspection for having a burr or sharp edge. Fillets also have lower stress concentration factors, meaning that they distribute stress over a broader area. This makes filleted parts more durable, and able to withstand larger loads.

Chamfers are more forgiving when designing to fit mating parts, but overall it appears that designs using fillets are preferred by senior management, industrial designers and many others.

The main points that help in deciding to choose a fillet or chamfer are the following:

1.When done manually one of the main factors that come in deciding which to apply is the machining time. A chamfer requires less machining time that a fillet radius.

2.When done on CNC both chamfer and fillet require the same time as only a tool change is required.

3.For fillets different radii of tools has to be stocked to create different radii, but a single tool can be used for creating different chamfers.

4.Higher machining time required translates into cost. Thus chamfers are less costly compared to fillets.

5.Industrial designers tend to prefer fillets compared to chamfers as these are considered to be visually pleasing.

6.One of the other reasons is that protective coating like paint are more uniformly distributed over a fillet compared to chamfer. Thickness of coating is reduced on sharp corners of chamfers so coating is lost first on these spots. Fillets have no such issues due to uniform distribution of coating.

7.Since non uniform distribution of coating can lead to accelerated rusting this may be a disadvantage.

8.Fillet gives better stress flow (less resistance) compared to chamfers. Fillets generally give a lower stress concentration factor than chamfers .

9. Chamfers are more forgiving when fitting mating parts. i.e. even if there are inaccuracies in a chamfer mating parts might fit together. But if the radius of fillet changes it will be difficult to fit the mating parts.